Coil-spring.



J. B. KNUDSEN.

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COIL-SPRING.

Specification of Letters Patent.

Patented April 13, 1909.

Application' led November 16, 1907. Serial No. 402,520.

To all 'whom it 'may concern:

Be it known that I, JACOB B. KNUDsEN, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinols, have invented new and useful Im rovements in Coil-Springs, of which the fol owing is a full, clear,'concise, and exact description, reference being had to the accom anying drawing, forming a part of this speci 'cation My invention relates to coil springs, and contem lates improvements over earlier devices o this class whereby. certain defects therein, as hereinafter pointed out, are eliminated.

My invention inds its most advanta eous embodiment in springs which are emp oyed to support very heavy structures. Of this class are car springs which are dis osed between the car body and axle to a sorb the jars and jolts which would otherwise be communicated from the wheels to the car.

In the earlier art coiled car s rings were usually constructed of material ci) quite large dimensions so that substantial support for the car could be aii'orded. It was found, however, that these springs could be given sufficient resiliency for the purpose for which they were to be used only by making the s iral of large and impractical diameter, and that when the diameter of the spiral was reduced to a more practicable size, the spring almost `entirely lost its yielding characteristics. In order to overcome these difiiculties and to provide more practical and serviceable springs, it became4 the practice to construct and use what is now knoan as a nest of springs. This improved structure consisted of a plurality of coiled springs of dierent diameters, each disposed within the next in order. 'Ihe dimensions ofthe material of which the springs were constructed varied also in the different springs, and the relation between the diameters of the spirals and the dimensions of the material of which the springs were constructed, was such that diameters. The sup orting strength would be the aggregate of t `e-supporting strength of all the springs. Being interdisposed, as pointed out, a compact device of practical size is obtained.

While the desired result of proper resiliency and sufficient su port was obtained in the prior art devices albove described, it has been found that such devices, being complicated, necessitated theexpenditure of considerablc time, labor and expense in con- .struction and involved complications in applying the same'to their. practical use.

It is the object of my invention, therefore, to provide a structure which will have the desirable characteristic of resiliency and the necessary supporting qualities, but which will not involve the disadvantages presented by the use of a nest of springs. To this end I provide 'a resilient structure which consists of but a single spiral bar, and my invention resides in the particular form of the bar. By the form of the spiral bar I mean the particular shape of a transverse section thereof. The shape of such a transverse section is such that the bar has greater thickness toward the outside of the spiral than at the inside, that is, the thickness of the bar diminishes from the outside of the spiral toward the inside. Thus, as the diameter of the coil decreases, the thickness of the bar also decreases and the rate of decrease may be such that, as the diameter decreases, the thickness of the bar is decreased in such proportion as to compensate therefor and thus maintain the same coeilicient of resiliency throughout.

In the accompanying drawings, Figure 1 is an elevational view of a coil spring embodying the features of my invention Fig. 2 is a plan view thereof and Fig. 3 isa longitudinal sectional view on the line 3 3 of Fig. 2.

The structure consists of a spiral bar 10, the outer part of which is considerably thicker than the inner part. While the particular form illustrated is not essential, I have, in the drawings, shown 'the bar 10 to be of approximately trapezoidal cross-section, the outer side 11 being the base of the trapezoid and the inner side 12 being the top thereof. The rate of decrease in thickness of the bar from the outer to the inner side must,

to attain the greatest theoretical efiiciency,

be properly proportioned to maintain the same 'coefficient of resiliency throughout the various intermediate thicknesses of the bar,

but I have found it sufficient and most practical to determine this rate of decrease approximately and Without theoretical and mathematical precision. I have found it suf.l iiciently accurate in practice to form this bar so that a radial line coincident with one side 13 will intersect a similar line coincident with the opposite surface 14 at the axis 15, as in dicated in dotted lines at 16. This is merely an exemplary method of determining the rate of decrease in the thickness of the bar approximately and practically, therefore I do not wish to be understood as defining or limiting my invention by such practice.

My invention involves thev broad proposition that the thickness of the bar decreases toward the center of the coil so as to compensate, by decreasing the amount of resisting material, for the increase in stiffness of the individual convolutions, resulting from the decrease in diameter.

I claim as new and desire to securevby -Letters Patent:

1. A resilient structure consistingfof a lspirally curved bar the thickness of which decreases toward the inside of the spiral sub# stantially proportionately with the decrease in diameter.

2. A resilient structure consisting of a spirally curved bar having upper and lower faces which, if extended, would meet in a common point inthe axis of the spiral.

3. A resilient structure comprising a spirally curved bar the thickness of which decreases toWard the inside of the spiral at such a rate as to maintain substantially the same coeflicient of resiliency of the structure at alll distances rom the-center of the spiral.

4. A resilient structure consisting of a spirally curved bar of substantially trapezoidal cross-section, the thickness of said bar decreasing from the outside diameter toward the inside diameter thereof with the decrease in diameter. i

In witness whereof, I have hereunto subscribed my name. in the presence of two wit- Ile'SSeS.

JACOB B. KNUDSEN. Witnesses: M. L. FARRAR, CHARLES L. HOPKINS. 

